Hybrid magnesium cement and method of manufacture

ABSTRACT

A hybrid magnesium cement composition formed of an A-side and a B-side. The A-side having an A1-component including a light-burn grade magnesium-containing material, and an A2-component including a non-metallic oxide salt. A B-side having a metal silicate polymer is included.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. provisional application Ser.No. 61/503,228 filed Jun. 30, 2011, which is incorporated in itsentirety herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The invention was made with Government support under Contract No.IIP-1113525. The Government has certain rights to the invention.

TECHNICAL FIELD

This application relates to a hybrid magnesium cement and a method ofmanufacture of same.

BACKGROUND OF THE INVENTION

Portland cement has been used in concrete for nearly two centuries. But,Portland cement generally requires energy-intensive productionfacilities sufficient to process limestone at 2,000° F. in mammothkilns. About one pound of carbon dioxide is released to the atmospherefor every pound of Portland cement produced. While Portland cement isused in many concrete structures, Portland cement also contributessignificantly to decay of installed infrastructure as Portland cementdeteriorates, especially due to attack from chloride ions.

Magnesium cement is suitable as a substitute for Portland cement. Atpresent, magnesium cements are derived from magnesium oxide and aretherefore relatively costly and relatively complicated products.Marketed products involving magnesium cement are primarily limited tothe interior wall applications, such as magnesium oxychloride cementboards. Magnesium oxychloride cement experiences a strength loss whenwet as a result of leaching of magnesium chloride and other chloridecomponents. Another magnesium cement, magnesium oxysulfate cement, alsoloses strength when wet because it still has a relatively significantmagnesium chloride component. Such strength reduction is a majorobstacle to other structural uses of magnesium cement. Other magnesiumcements provide high performance, but have limited raw materialsupplies, cannot be wet-cured, and are otherwise ten-fold more expensivethan Portland cement.

A more sustainable material is needed to replace Portland cement,especially a material has superior mechanical properties and duty life,especially in wet duty service, while being reasonably priced.

SUMMARY OF THE INVENTION

In at least one embodiment, a hybrid magnesium cement composition isformed of an A-side having an A1-component including a light-burn grademagnesium-containing material, and an A2-component including anon-metallic oxide salt. A B-side having a metal silicate polymer isincluded.

In at least one embodiment, a method of manufacture of a hybridmagnesium cement composition includes calcining a magnesium-containingmaterial at a temperature in a range of 770° C. to 1,100° C. for a timeperiod ranging from 0.2 hr to 2.5 hr to form a light-burn grademagnesium-containing material (LGBM). The method also includes mixingthe LGBM with a non-metallic oxide salt to form amagnesium-oxide-non-metallic oxide salt (MONMO) inorganic polymer. TheMONMO is mixed with a metal silicate polymer to form a dry hybridmagnesium-containing composition.

In another embodiment, a light-burn grade magnesium-containing material(LGBM) composition includes calcium carbonate present in the range of 30wt. % to 70 wt. % of the LGBM, calcium oxide in an amount less than 10wt. % of the LGBM, magnesium carbonate in an amount less than 25 wt. %of the LGBM, and magnesium oxide present in an amount ranging from 18wt. % to 70 wt. % of the LGBM. The composition totals 100 wt. % of theLBGM, excluding other components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 graphically illustrates a time versus temperature graph ofcalcining of magnesium-containing materials according to at least oneembodiment; and

FIG. 2 diagrammatically illustrates a method of making a hybridmagnesium-containing cement according to at least one embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Reference will now be made in detail to presently preferredcompositions, embodiments and methods of the present invention, whichconstitute the best modes of practicing the invention presently known tothe inventors. The figures are not necessarily to scale. However, it isto be understood that the disclosed embodiments are merely exemplary ofthe invention that may be embodied in various and alternative forms.Therefore, specific details disclosed herein are not to be interpretedas limiting, but merely as a representative basis for any claims and/oras a representative basis for teaching one skilled in the art tovariously employ the present invention.

Except in examples, or where otherwise expressly indicated, allnumerical quantities in this description used to indicate amounts ofmaterial or dimensions are to be understood as modified by the word“about” in describing the broadest scope of the invention. Practicewithin the numerical limits stated is generally preferred. Also, unlessexpressly stated to the contrary: the description of a group or class ofmaterials as suitable or preferred for a given purpose in connectionwith the invention implies that mixtures of any two or more the membersof the group or class are equally suitable for preferred; the firstdefinition of an acronym or other abbreviation applies to all subsequentuses herein of the same abbreviation and applies mutatis mutandis tonormal grammatical variations of the initially defined abbreviation;and, unless expressly stated to the contrary measurement of a propertyis determined by the same technique as previously or later referencedfor the same property. Also, unless expressly stated to the contrary,percentage, “parts of,” and ratio values are by weight, and the term“polymer” includes “oligomer,” “copolymer,” “terpolymer,” “pre-polymer,”and the like.

A hybrid magnesium cement, in at least one embodiment, is formed bymixing a Part A: a magnesium-containing material that includes magnesiumoxide with a Part B: a metal silicate polymer. Before mixing to form thehybrid magnesium cement, the magnesium-containing material and the metalsilicate polymer are each partially reacted separately, forming apartially-cured magnesium-containing material and a partially-curedmetal silicate polymer. Part A is a mixture of a Part A1: a light-burngrade magnesium-containing material, and a Part A2: a non-metallic oxidesalt.

Turning now to FIG. 1, a time versus weight loss graph is shown ofcalcining of the magnesium-containing material according to at least oneembodiment. In the embodiments of FIG. 1, a dolomite is themagnesium-containing material. At line 10 is the weight loss trace ofcalcining the dolomite at 900° C. The weight loss equivalent to thestoichiometric amount of carbon dioxide from the decomposition ofmagnesium carbonate in the dolomite to magnesium oxide is reached inapproximately 45 minutes. Faster temperature rise favors maximizingconverting only magnesium carbonate and not calcium carbonate in thedolomite which is preferable for later forming amagnesium-oxide-non-metallic oxide salt inorganic polymer (MONMO), amagnesium-containing cement mortar, a partially-curedmagnesium-containing cement mortar, and the hybrid magnesium cement.Faster processing of the dolomite to the stoichiometric maximum loss ofcarbon dioxide, line 14 of FIG. 1, from the decomposition of magnesiumcarbonate is advantageous from a manufacturing cost perspective withless energy used and a better utilization rate of a calciner relative toa longer calcining time with a conventional Portland cement calciningoperation. At line 12 is the weight loss trace of calcining the dolomiteat 850° C. The loss of the stoichiometric amount of carbon dioxide fromthe decomposition of magnesium carbonate in the dolomite to magnesiumoxide is reached in approximately 115 minutes. At line 16 is the weightloss trace of calcining the dolomite at 750° C. The loss of thestoichiometric amount of carbon dioxide from the decomposition ofmagnesium carbonate in the dolomite to magnesium oxide is not achieved.At line 18 is the weight loss trace of calcining the dolomite at 600° C.The loss of the stoichiometric amount of carbon dioxide from thedecomposition of magnesium carbonate in the dolomite to magnesium oxideis never achieved. It should be understood that in other embodimentsusing different materials and equipment, other temperature settings mayachieve the maximum stoichiometric decomposition of magnesium carbonate.It is also understood that other temperature and equipment combinationsmay achieve hybrid cements having lesser, but still acceptable,performance properties for the intended use.

It is understood that there are substantial variations in magnesium,calcium, and contaminant amounts in naturally occurring dolomite. In anominal dolomite, calcium is present in an amount of 54.3 wt. % CaCO₃and magnesium is present in an amount of 45.7 wt. %. Dolomite variationsfrom nominal contemplated within the scope of this invention include,but are not limited to, a calcitic dolomite, a dolomitic limestone, amagnesium limestone, a steel-melting-shop grade of dolomite, and ablast-furnace grade of dolomite.

In at least one embodiment the light-burn grade magnesium-material has acomposition as shown in Table 1A, where the composition accumulates to100%.

TABLE 1A MINIMUM MAXIMUM COMPONENT AMOUNT (%) AMOUNT (%) CaCO₃ 30 70 CaO0 10 MgCO₃ 0 25 MgO 18 70 Other 0 12

In another embodiment the light-burn grade magnesium-material has acomposition as shown in Table 1B, where the composition accumulates to100%.

TABLE 1B MINIMUM MAXIMUM COMPONENT AMOUNT (%) AMOUNT (%) CaCO₃ 40 65 CaO0.1 7.5 MgCO₃ 0 10 MgO 30 60 Other 0.1 7

In another embodiment the light-burn grade magnesium-material has acomposition as shown in Table 1C, where the composition accumulates to100%.

TABLE 1C MINIMUM MAXIMUM COMPONENT AMOUNT (%) AMOUNT (%) CaCO₃ 50 60 CaO0.2 5 MgCO₃ 0 5 MgO 40 50 Other 0.1 7

In at least one embodiment, the weight ratio in the light-burn grademagnesium-containing material of MgCO₃ to MgO ranges from 0 to 0.71. Inanother embodiment, the weight ratio of the light-burn grademagnesium-containing material MgCO₃ to MgO ranges from 0.01 to 0.55. Inyet another embodiment, the weight ratio of the light-burn grademagnesium-containing material MgCO₃ to MgO ranges from 0.05 to 0.20.

In at least one embodiment, in forming light-burn grademagnesium-containing material, essentially all MgCO₃ in the raw materialis transformed by calcining into MgO as measured by weight between theinitial dried material and the after-calcining, colled dried material.In another embodiment, in forming light-burn grade magnesium-containingmaterial essentially all MgCO₃ in the raw material is transformed bycalcining into MgO and essentially none of the CaCO₃ in the raw materialis converted into CaO. In another embodiment, in forming light-burngrade magnesium-containing material essentially all MgCO₃ in the rawmaterial is transformed by calcining into MgO and less than 20 rel. % ofthe CaCO₃ in the raw material is converted into CaO. In anotherembodiment, in forming light-burn grade magnesium-containing materialessentially all MgCO₃ in the raw material is transformed by calcininginto MgO and less than 10 rel. % of the CaCO₃ in the raw material isconverted into CaO. In another embodiment, in forming light-burn grademagnesium-containing material at least 80 rel. % of MgCO₃ in the rawmaterial is transformed by calcining into MgO and less than 20 rel. % ofthe CaCO₃ in the raw material is converted into CaO. In anotherembodiment, in forming light-burn grade magnesium-containing material atleast 90 rel. % of MgCO₃ in the raw material is transformed by calcininginto MgO and less than 20 rel. % of the CaCO₃ in the raw material isconverted into CaO. In another embodiment, in forming light-burn grademagnesium-containing material at least 90 rel. % of MgCO₃ in the rawmaterial is transformed by calcining into MgO and less than 10 rel. % ofthe CaCO₃ in the raw material is converted into CaO.

In at least one embodiment, the magnesium-containing material is thedolomite that is calcined to form a light-burn grade dolomite. Thelight-burn grade dolomite is calcined at temperature for a time periodranging from 0.2 hours to 2.5 hours. In another embodiment, thelight-burn grade dolomite is a calcined at temperature for a time periodranging from 0.5 hours to 2 hours. In another embodiment, the light-burngrade dolomite is calcined at temperature for a time period ranging from0.75 hours to 1.5 hours.

The magnesium-containing material, in at least one embodiment, is thelight-burn grade dolomite formed by calcining a dolomite at atemperature ranging from 770° C. to 1,100° C. In another embodiment, thelight-burn grade dolomite is formed by calcining the dolomite at atemperature ranging from 800° C. to 950° C. In yet another embodiment,the light-burn grade dolomite is formed by calcining the dolomite at atemperature ranging from 850° C. to 900° C. It was surprising that anexceptionally and unacceptably violent reaction occurs when thelight-burn grade dolomite is calcined at temperatures at or above 1,100°C. and subsequently mixed with a non-metallic oxide salt.

In at least one embodiment, the mixture of light-burn grade dolomitewith the non-metallic oxide salt forms a magnesium-oxide-non-metallicoxide salt inorganic polymer (MONMO). MONMO is reactable with the metalsilicate polymer to form the hybrid cement in certain embodiments.

In at least one embodiment, the non-metallic oxide salt is a sulfatesalt. In another embodiment, the non-metallic oxide salt is a phosphatesalt.

In at least one embodiment, the phosphate salt is a soluble phosphate.In another embodiment, the phosphate is a crystalline phosphate.Non-limiting examples of the phosphate salt include metal dihydrogenphosphate, dimetal hydrogen phosphate, metal phosphate, where the metalis a monovalent metal cation, such as potassium. In another embodiment,the phosphate salt may include phosphate compositions having ammonium,alkaline earth and/or di- and/or trivalent metal cations.

In at least one embodiment, the weight ratio of the non-metallic oxidesalt to the magnesium oxide in the light-burned grade dolomite rangesfrom 0.1 to 1.2. In another embodiment, the weight ratio of thenon-metallic oxide salt to the magnesium oxide in the light-burned gradedolomite ranges from 0.3 to 1.1. In yet another embodiment, the weightratio of the non-metallic oxide salt to the magnesium oxide in thelight-burned grade dolomite ranges from 0.5 to 0.95. It is unexpectedthat the weight ratio of non-metallic oxide salt to magnesium oxide issignificantly different from the stoichiometric ratio. Without beingtied to any one theory, this unexpected result may arise from the broaddistribution of particles sizes of the light-burn grade dolomite, wherethe large particle sizes do not receive all of the reactants during therelative short reaction time period.

Besides temperature and residence time in a calciner, the particle sizemay contribute to the magnesium-containing material's effectiveness inthe hybrid cement. The particle size distribution of the dolomite, in atleast one embodiment, has more than 85 wt. % being less than a TylerEquivalent 100-mesh screen and less than 15 wt. % being less than a 4.8μm particle size when measured according to ASTM D422-07. In anotherembodiment, the particle size distribution of the dolomite has aparticle size distribution with more than 90 wt. % being less than aTyler Equivalent 100-mesh screen and less than 15 wt. % being less thana 15.8 μm particle size. In yet another embodiment, particle sizedistribution of the dolomite has with more than 95 wt. % being less thana Tyler Equivalent 100-mesh screen and less than less than 15 wt. %being less than a 36.2 μm particle size.

The light-burn grade dolomite particle size distribution, in at leastone embodiment, has more than 85 wt. % being less than a TylerEquivalent 100-mesh screen and less than 15 wt. % being less than a 4.8μm particle size when measured according to ASTM D422-07. In anotherembodiment, the particle size distribution of the light-burn gradedolomite has a particle size distribution with more than 90 wt. % beingless than a Tyler Equivalent 100-mesh screen and less than 15 wt. %being less than a 15.8 μm particle size. In yet another embodiment, theparticle size distribution of the light-burn grade dolomite has withmore than 95 wt. % being less than a Tyler Equivalent 100-mesh screenand less than less than 15 wt. % being less than a 36.2 μm particlesize.

In another embodiment, there is a surprising synergy between arelatively rapid heating rate and the ultimate heating temperature, withthe objective of maximizing the formation of magnesium oxide whileminimizing the calcium oxide formed. Other process parameters, such asparticle size and surface area, and the mineral mixture of the sourcematerial play roles in this surprising synergy. One surrogate measure ofthe synergy is the amount of carbon dioxide and other mass componentsbeing driven off the raw materials during calcining.

During the calcining of the light-burn grade dolomite, in at least oneembodiment, the light-burn grade dolomite experiences a weight lossranging from 23-28 dry weight percentage relative to an uncalcineddolomite. In another embodiment, the light-burn grade dolomiteexperiences a weight loss ranging from 24-27 dry weight percentagerelative to an uncalcined dolomite. In yet another embodiment, thelight-burn grade dolomite experiences a weight loss ranging from 25-26dry weight percentage relative to an uncalcined dolomite. It ispreferable that the weight loss measured be weight lost frommagnesium-containing materials releasing carbon dioxide while formingmagnesium oxide. In at least one embodiment, the carbon dioxide amountreleased from magnesium-containing materials ranges from 60 wt. % of thetotal weight loss to 95 wt. % of the total weight loss. In anotherembodiment, the carbon dioxide amount released from magnesium-containingmaterials ranges from 70 wt. % of the total weight loss to 90 wt. % ofthe total weight loss. In another embodiment, the carbon dioxide amountreleased from magnesium-containing materials ranges from 75 wt. % of thetotal weight loss to 85 wt. % of the total weight loss.

In another embodiment, the carbon dioxide amount released frommagnesium-containing materials ranges from 70 wt. % to 120 wt. % of thestoichiometric maximum weight loss of magnesium carbonate. An exemplarycalculation of the stoichiometric maximum weight loss is as follows: inat least one embodiment, a dolomite blend includes 51 wt. % calciumcarbonate (CaCO₃) and 42 wt. % magnesium carbonate (MgCO₃). The molarmass of CaCO₃ is 100 g and CaO is 56 g. The molar mass of MgCO₃ is 84.5g and for MgO is 40 g. In a 100 g sample of a representative blend ofdolomitic materials, there is 42 g of MgCO₃. After a heating timeperiod, the dolomite magnesium theoretically decomposes only MgCO₃ toonly MgO, the sample would weigh 40/84.5 of the original amount 47.3% ofthe original MgCO₃ mass or 19.9 g MgO. The resultant weight oflight-burn grade dolomite is, therefore, only (51+19.9)/(51+42) or 76%of the original weight. Stated as the stoichiometric loss of carbondioxide, i.e. 100 wt. %-76 wt. %, that is 24 wt. % loss. In anotherembodiment, the carbon dioxide amount released from magnesium-containingmaterials ranges from 80 wt. % to 110 wt. % of the stoichiometricmaximum mass loss of magnesium carbonate. In another embodiment, thecarbon dioxide amount released from magnesium-containing materialsranges from 90 wt. % to 105 wt. % of the stoichiometric maximum massloss of magnesium carbonate.

Calcining of the dolomite may occur using heating techniques known inthe art. Non-limiting examples of heating techniques include a staticoven method, a static oven method with preheating, a calciner method, acalciner process with preheating, a dielectrically-heated method, and amicrowave-heated method.

It was surprising that the light-burn grade dolomite, when formed intothe magnesium cement, experienced reduced tensile strength by as much as50% relative to the magnesium cement formed with the light-burn gradedolomite that did not experience a weight loss as in the ranges above.

It is understood that while the examples have been presented inembodiments involving dolomite, other magnesium-containing minerals aresuitable for use in certain other embodiments without exceeding thescope and limitations of the contemplated invention. Non-limitingexamples of other magnesium-containing materials include pyroxenite,amphibolite, serpentine, dunite, and chlorite.

In at least one embodiment, when a portion of calcium oxide is formedduring calcining, especially above 1,000° C., the reaction of thecalcium oxide with the metal silicate polymer can be hazardouslyexothermic. The excess calcium oxide can be retarded with a preliminaryaddition of water to form a hydrated lime (Ca(OH)₂) prior to mixing withthe metal silicate polymer.

In at least one embodiment, the magnesium-containing material haschloride present in a maximum amount of 10 wt. % chloride content. Inanother embodiment, the magnesium-containing material has chloridepresent in a maximum amount of 5 wt. % chloride content. In anotherembodiment, the magnesium-containing material has chloride present in amaximum amount of 2 wt. %.

In another embodiment, the magnesium-containing material may be retardedusing a set retarder such as boric acid or borax. In at least oneembodiment, the retarded magnesium-containing material may be alsoun-retarded by addition of materials to neutralize or sequester theboron-containing compounds.

A dolomite cement mortar is formed from the light-burn grade dolomite,phosphate salt, a first latent hydraulic additive, a second latenthydraulic additive, water, and sand. The dolomite cement mortar isreacted with the metal silicate polymer to form the hybrid cement in atleast one embodiment.

The dolomite cement mortar composition, in at least one embodiment,includes the formulation in Table 2, as follows, where the compositiontotals 100 wt. %:

TABLE 2 Component Minimum Wt. % Maximum Wt. % Light-Burn Grade Dolomite¹24 39 Potassium Dihydrogen Phosphate 2.7 4.5 First Latent HydraulicAdditive² 19 30 Second Latent Hydraulic Additive³ 1.3 2.5 Sand⁴ 19 30Water 9 15 ¹Raw Dolomite supplied by Osborne Materials Co., DrummondIsland, MI ²Ground Granulated Blast-Furnace Slag (GGBFG) ³Silica Fume⁴White silica sand-fine particle size

In at least one embodiment, the reaction of the magnesium-containingmaterial with the metal silicate is too rapid for good mixing.Unexpectedly, the rapid reaction results in damage to the molds,relatively poor workability, relatively low hardened strength, andrelatively large granularity of the dolomite cement mortar. The additionof the GGBFG to the magnesium-containing material results in arelatively slower reaction rate, in at least one embodiment. Inaddition, having the GGBFG in the composition lowers the heat ofhydration and lower temperature increases during the mixing of thedolomite cement mortar in certain embodiments. GGBFG, in certainembodiments, also reduces the occurrence of microcracking in thedolomite cement mortar because of reduced thermal gradients during thecuring of the dolomite cement mortar.

The metal silicate polymer, at least one embodiment, is formed by aninorganic polymerization reaction at the nano-structure condition in agelled state using a relatively low temperature regime of less than 100°C. Such a condition leads to formation of longer inorganic chains andloosely cross-linked chains in acidic regimes with elevated reagentconcentrations. Rings, cluster networks, and cages are included in thebasic regimes with relatively low reagent concentrations. In at leastone embodiment, a silica-containing compound is reacted with a hydroxideanion using a water glass reaction at relatively high reagentconcentrations in a very basic pH regime defined by 3.7 wt. % anhydroussodium hydroxide anion to form an aluminum silicate inorganic polymer.The silica-containing compounds include silicates known in the art to bewastes without many current use applications. Non-limiting examples ofsilicate-containing compounds include a municipal incineration ash, abiomass ash, a silicate glass, a ground glass, mine tailings, andmixtures thereof. Non-limiting examples of biomass ash include ash fromcombustion of rice, husks, straw, algae, or switchgrass. Non-limitingexamples of the silicate glass include sodium silicate, fly ash, class Cfly ash, class F fly ash, silica fume, high-reactivity metakaolin, blastfurnace slag, and bottom ash, especially bottom ash ground to an averageparticle size ranging from less than 100 Tyler mesh to 4.8 μm. Theunexpected ability to use bottom ash is advantageous despite itsrelative inertness, especially because of the large amount ofessentially unusable bottom ash waste material that is available.

In at least one embodiment, the hydroxide anion is present in an amountranging from 7 weight percent in solution to a saturated hydroxide anionsolution. Non-limiting examples of hydroxide anion include sodiumhydroxide anion, ammonium hydroxide anion, magnesium hydroxide anion andcalcium hydroxide anion, preferably calcium hydroxide formed byhydration of calcium oxide in the magnesium-containing material. Use ofcalcium oxide or hydroxide anion from the magnesium-containing materialis unexpectedly advantageous in reducing cost and the use of low-valuematerials in forming the metal silicate polymer when the polymer iscombined with the magnesium-containing material. The hydration ofcalcium oxide surprisingly transformed the excessive amount and rate ofenergy released when amounts of calcium oxide are reacted with thephosphate salts into a useful source of hydroxide anion with anacceptably lower amount and controllable rate of energy release duringthe reaction. In at least one embodiment, calcium oxide in thelight-burn grade dolomite is present at less than 5 wt. % of thelight-burn grade dolomite. In another embodiment, calcium oxide in thelight-burn grade dolomite is present at less than 9.5 wt. % of thelight-burn grade dolomite.

In at least one embodiment, the metal silicate polymer is present in anamount ranging from 65 wt. % to 97 wt. % of the metal silicate polymercomposition. In another embodiment, the metal silicate polymer ispresent in an amount ranging from ranging from 75 wt. % to 93 wt. % ofthe metal silicate polymer composition. In yet another embodiment, themetal silicate polymer is present in an amount ranging from 80 wt. % to90 wt. % of the metal silicate polymer composition. A non-limitingexample of the metal silicate polymer includes an aluminosilicateinorganic polymer.

In at least one embodiment, the metal silicate polymer composition isgiven in the range in Table 3, as follows, where the composition totals100 wt. %:

TABLE 3 Component Minimum Wt. % Maximum Wt. % Strong Base¹ 2.8 4.5Supplementary Cementitious 6.5 10.5 Material Accelerator² Silicate³ 2037 Second Latent Hydraulic Additive⁴ 2 3.5 Sand⁵ 35 55 Water 9 15¹Sodium Hydroxide anion, anhydrous ²A complex amorphous structurecomposition having long-range order including aluminum atoms, siliconatoms, and oxygen atoms, including the metakaolin ³A silicate-calciumoxide source: Class F Flyash supplied by Boral Material Technologies,San Antonio, TX ⁴Silica Fume ⁵White silica sand-fine particle size

In at least one embodiment, an additive is included in the hybridmagnesium cement composition or components thereof. Non-limitingexamples of the additive include a supplemental oxide, such as an ironoxide; a chemical activator, such as sodium sulfate; a superplasticizer,such as a sulfonated composition; a lightening agent, such ascenospheres; a foaming agent, such as an inorganic foaming agent; astabilization agent; a fiber reinforcement, such as a short fiber or acontinuous fiber; and a filler, such as a sand and/or an aggregatefiller forming a hybrid magnesium concrete.

In at least one embodiment, when MOP is reacted with the metal silicatepolymer, a silicon phosphate, a non-limiting example of which is SiP₂O₇that forms as a crystal. In at least one embodiment, the crystal is aneedle-shaped crystal having a relatively long chain length. Themalleability of MOP with the needle-shaped crystal significantly exceedsthe malleability observed in the art with relatively short chaincrystals of SiP₂O₇.

In at least embodiment, the silicon phosphate is present in an amount ofless than 3 wt. % of the silicon phosphate crystal. In anotherembodiment, the silicon phosphate is present in an amount ranging from0.1 wt. % to 2 wt. %. Without being confined to any one theory, thesilicon phosphate allows slippage along the inorganic polymer chain,advantageously improving the malleability of the hybrid cement relativeto Portland cement's ultimate compressive strain capacity of less than0.3%. In at least one embodiment, the hybrid cement has an ultimatecompressive strain capacity ranging from 0.5% to 3%. In anotherembodiment, the hybrid cement has an ultimate strain capacity rangingfrom 0.8% to 2.5%.

A soluble phosphate salt may be ground and mixed in with the dry hybridmagnesium-containing cement composition, forming shotcrete-dry mix, inat least one embodiment. In another embodiment, the soluble phosphatesalt may be dissolved in water which is then mixed with the dry hybridmagnesium cement composition forming shotcrete-wet mix. It is surprisingthat the soluble phosphate salt accelerates the polymerization of thehybrid magnesium cement composition to a point where the mixture isunworkable after a time period ranging from 30 seconds to 5 minutes. Theamount of phosphate salt in at least one embodiment, ranges from 0.5weight percent to 20 weight percent of the hybrid magnesium cementcomposition. In another embodiment, the phosphate salt is present in anamount ranging from 2 weight percent to 15 weight percent of the hybridmagnesium cement composition. In yet another embodiment, the phosphatesalt is present in an amount ranging from 5 weight percent to 10 weightpercent of the hybrid magnesium cement composition.

In at least one embodiment, the reinforcement includes a short fiberhaving a length ranging from 0.06 inches to 1 inch. In anotherembodiment, the short fiber has a length ranging from 0.25 inch to 0.75inch. In another embodiment, reinforcement includes a continuous fiberincluding a woven reinforcement and/or a nonwoven reinforcement.

In at least one embodiment, the reinforcement includes a fiber having ametal composition. In another embodiment, the reinforcement includes afiber having a ceramic composition, such as a glass fiber. In yetanother embodiment, the reinforcement includes a fiber having an organiccomposition, such as a natural fiber, an aramid fiber, a carbon fiber, apolypropylene fiber or a nanotube.

In at least one embodiment, the reinforcement includes a crenulatedfiber. In another embodiment, reinforcement includes a milled fiber. Inyet another embodiment, the reinforcement includes an extruded fiber.

In at least one embodiment, aggregate is added with the sand to form amagnesium concrete. In at least one embodiment, the aggregate is gravel.The aggregate, in at least one embodiment, is added to the magnesiumcement composition in an amount ranging from 25 volume percent to 50volume percent of the magnesium cement composition before the sand andaggregate is added. In another embodiment, the aggregate is added to themagnesium cement composition in an amount ranging from 35 volume percentto 45 volume percent.

In at least one embodiment, the ratio of sand to gravel in the magnesiumcement composition ranges from 0.5 to 0.75. In another embodiment, theratio of sand and gravel in the magnesium cement composition ranges from0.6 to 0.7. In at least one embodiment, when the magnesium cementcomposition, sand, and gravel are mixed the magnesium concrete isformed.

EXAMPLES Example 1

A sample magnesium-containing cement mortar is prepared with 1 partmagnesium oxide in a light-burn grade dolomite, 1 part GGBFS, and 0.1part tripotassium phosphate. A sample of a metal silicate polymer isprepared with 1 part Class F fly ash, and 0.13 parts sodium hydroxideanion. Between the magnesium-containing cement mortar and the metalsilicate polymer, 1.9 parts of sand, 0.15 parts of silica, and 0.73parts of water are dispersed. The mixture is mixed thoroughly forming ahybrid magnesium-containing cement sample composition. The hydrationmechanism is not fully understood in this case, but is known to bedifferent than the hydration mechanism of Portland cement.

Example 2

The composition of Example 1 is cast into 40 mm×40 mm×40 mm molds. Thesamples are demolded after 24 hours. After three days, the compressivestrength is measured at 35 MPa when tested to failure at a constantcross-head speed of 0.001 mm/sec according to test method ASTM C773-88(2011). After two weeks, the compressive strength achieves 50 MPa with avariability of +/−15%. The ultimate strain of the samples ranges from1.o % to 2.o%, which is at least three times the ultimate strain ofPortland cement. While not wishing to be bound by any one theory, theincrease in ultimate strain, i.e. the malleability, is believed to bethe result of the formation of needle-like crystals of SiP₂O₇ havingunexpectedly long polymeric chains.

Example 3

The composition of Example 1 is cast as a 3 mm plate. Short fibers,having an average length ranging from 1.6 mm to 60 mm, are added toExample 1 and are present in an amount ranging from 0.1 vol. % to 2 vol.%.

Example 4

The composition of Example 1 is cast as a 3 mm plate. Continuous fibers,having an average length ranging greater than 60 mm, are added toExample 1 and are present in an amount ranging from 0.1 vol. % to 5 vol.%.

Example 5

The samples of Examples 3 and 4, i.e. magnesium-containing hybridcements made with fibers unexpectedly show an ability to sustainincreasing loads beyond the first crack strength, thereby failingprogressively rather than catastrophically. The failure appears to bemore like the yielding of steel and is classified as pseudo-strainhardening. Catastrophic failure is typically expected of ceramics likethe hybrid magnesium-containing cement.

Example 6

Samples having the composition of Table 2, but with a weight ratio ofpotassium dihydrogen phosphate to dolomite of 0.3, are calcined andtested for compressive strength. The tests show that the maximumstrength observed is achieved at 900° C., and decreases as the dolomiteis calcined at 1,000° C., as shown in Table 4.

TABLE 4 Calcining Temperature (° C.) Average Compressive Strength (MPa)¹0 0 600 1.2 750 1.3 900 6.7 1,000 3.8 ¹Measured after 24 hr

Example 7

Samples having the composition of Table 2, but with a weight ratio ofpotassium dihydrogen phosphate to dolomite ranging from 0.1 to 0.9, arecalcined at 900° C. and tested for compressive strength. The tests showthat the maximum strength observed is achieved when the weight ratio isbetween 0.3 and 0.9 as shown in Table 5.

TABLE 5 Weight Ratio of Average Compressive KH₂PO₄ to dolomite Strength(MPa)¹ 0.1 1.5 0.2 4.8 0.3 6.7 0.9 6.2 ¹Measured after 24 hr

Turning now to FIG. 2, a method of manufacture of a hybridmagnesium-containing cement mortar is diagrammatically illustratedaccording to at least one embodiment. In step 100, themagnesium-containing material, such as the dolomite, is provided. Instep 102, the magnesium-containing material is calcined at 770° C. to1,100° C. for 0.2 hours to 2.5 hours forming the light-burn grademagnesium-containing material. In step 104, the light-burn grademagnesium-containing material is mixed with the soluble phosphate saltforming the MOP. In step 106, the MOP is mixed with a silicate to formthe magnesium-containing cement mortar without water. In step 108,magnesium-containing cement mortar is partially cured as result ofmixing with water forming a partially-cured magnesium-containing cementmortar. In step 110, an uncured metal silicate polymer precursor isprovided, such as the formulation in Table 3 without the water. Uponaddition of water, in step 112, the metal silicate polymer precursorpartially cures forming a partially-cured metal silicate polymer. Instep 114, the partially-cured magnesium-containing cement mortar and thepartially-cured metal silicate polymer are mixed to form the hybridmagnesium-containing cement.

While embodiments of the invention have been illustrated and described,it is not intended that these embodiments illustrate and describe allpossible forms of the invention. Rather, the words used in thespecification are words of description rather than limitation, and it isunderstood that various changes may be made without departing from thespirit and scope of the invention.

What is claimed is:
 1. A magnesium-containing material composition,comprising: calcium carbonate present in an amount ranging of 30 wt. %to 70 wt. % of the magnesium-containing material composition; calciumoxide in an amount less than 10 wt. % of the magnesium-containingmaterial composition; magnesium carbonate in an amount less than 25 wt.% of the magnesium-containing material composition; and magnesium oxidepresent in an amount ranging from 18 wt. % to 70 wt. % of themagnesium-containing material composition, wherein the compositiontotals 100 wt. % of the magnesium-containing material composition,excluding other components.
 2. The magnesium-containing materialcomposition of claim 1, comprising: calcium carbonate present in anamount from 40 wt. % to 65 wt. % of the magnesium-containing materialcomposition; calcium oxide present in an amount from 0.1 wt. % to 7.5wt. % of the magnesium-containing material composition; magnesiumcarbonate in an amount less than 10 wt. % of the magnesium-containingmaterial composition; and magnesium oxide present in an amount from 30wt. % to 60 wt. % of the magnesium-containing material composition,wherein the composition totals 100 wt. % of the magnesium-containingmaterial composition, excluding other components.
 3. Themagnesium-containing material composition of claim 1, comprising:calcium carbonate present in an amount from 50 wt. % to 60 wt. % themagnesium-containing material composition; calcium oxide present in anamount from 0.2. wt. % to 5 wt. % of the magnesium-containing materialcomposition; magnesium carbonate in an amount less than 5 wt. % of themagnesium-containing material composition; and magnesium oxide presentin an amount from 40 wt. % to 50 wt. % of the magnesium-containingmaterial composition, wherein the composition totals 100 wt. % of themagnesium-containing material composition, excluding other components.4. The magnesium-containing material composition of claim 1, furthercomprising sand.